Underwater guns are useful as anti-mine and anti-torpedo devices. Recently, autonomous underwater vehicles (AUVs) have been fitted with underwater guns for torpedo defense and underwater “hunter-killer” CONOPs.
A gun, especially one with a high muzzle velocity, cannot be fired when water is in its barrel. If a firing where to incur in a water-filled barrel, a very high breach pressure would result as the ignited propellant charge forces (or tries to force) the water out of the barrel. The likely result would be material failure of the barrel.
The prior art is replete with approaches for waterproofing the barrel of an underwater gun, or for clearing water from its barrel before firing. U.S. Pat. No. 5,639,982 discloses a means for firing a fully automatic gun underwater using a blank barrel-clearance round. Blank barrel-clearance rounds are alternated with live rounds of ammunition. To begin the process, a blank barrel-clearance round is first detonated. This creates gas and steam within the chamber that forms a bubble at the muzzle end of the barrel, thereby displacing water from the chamber. A live round is then immediately fired. The process is repeated, whereby the subsequent detonation of a blank barrel-clearance round displaces any water that has re-entered the barrel subsequent to the firing of the live round.
U.S. Pat. No. 5,648,631 discloses a spooled tape seal for sealing the barrel of an underwater gun. The system includes a tap that covers the opening of the gun barrel and sprockets for advancing the tape across the opening. Hydrostatic pressure keeps the tape pressed to the end of the barrel to create an effective seal. When a bullet is fired, it perforates the tape. During this brief period of egress, the exhaust gases from combustion of the propellant charge keep water from entering the barrel. Almost immediately, a non-perforated portion of the tape is advanced by the sprockets to cover the barrel opening. External hydrostatic pressure re-seats the tape, thereby preventing water from entering the barrel.
U.S. Pat. No. 5,687,501 discloses a sealing plate for providing a watertight seal for a multi- or single-barreled underwater gun. The sealing plate provides one or more firing apertures in an otherwise solid surface. Between firings, the gun muzzle is sealed by a solid surface of the sealing plate. To fire a bullet, the sealing plate or muzzle rotates to align the gun muzzle with one of the firing apertures. This permits unimpeded egress. After the bullet fires, the plate or muzzle again rotates so that a solid portion of the sealing plate covers the muzzle.
These are but a few of the many patents pertaining to various aspects of underwater gun design in general, and to the water-in-the-barrel problem, in particular. Notwithstanding the many approaches to the problem, no truly satisfactory approach has been developed for keeping water out of the barrel of an underwater gun between and during operation.